1. Field of the Invention
The present invention relates to a device for mass spectrometry that is used in a method for performing mass spectrometry. In the method, a sample (assay material) in contact with a surface of the device is irradiated with measurement light, and an analyte (analysis target) for mass spectrometry contained in the sample is desorbed from the surface of the device to perform mass spectrometry on the analyte. Further, the present invention relates to a mass spectrometry apparatus and a mass spectrometry method using the device for mass spectrometry.
2. Description of the Related Art
Mass spectrometry methods are used to identify a substance or the like, and a mass spectrometry method in which an analyte is desorbed from a device for mass spectrometry by irradiating a sample in contact with the device with measurement light and the desorbed analyte is detected for each mass is well known. For example, in a time-of-flight mass spectrometry method (Time of Flight Mass Spectroscopy: TOF-MS), the mass of a substance desorbed from a device for mass spectrometry is analyzed based on flight time of the substance by making the substance fly for a predetermined distance.
Ordinarily, in the mass spectrometry methods as described above, the analyte is ionized and desorbed from the device for mass spectrometry. However, particularly when the analyte is a sparingly volatile substance (or non-volatile substance), such as a bio-substance obtained from a living body, or a high-molecular-weight substance, such as a synthetic polymer, the analyte is neither easily ionized nor desorbed. Therefore, various methods for performing mass spectrometry on these kinds of substance have been studied.
In a matrix assisted laser desorption ionization method (MALDI method), an analyte is mixed into sinapic acid, glycerine or the like, which is called as a matrix, to obtain a mixed crystal, and the mixed crystal is used as a sample. Further, light energy absorbed by the matrix is utilized to vaporize the analyte together with the matrix. Further, the analyte is ionized by proton-transfer (proton movement) between the matrix and the analyte. The MALDI method is widely used in mass spectrometry of a sparingly volatile substance, a bio-molecule, a high-molecular-weight substance, such as a synthetic polymer, and the like (for example, Japanese Unexamined Patent Publication No. 9(1997)-320515 or the like), because the MALDI method is a soft ionization method that causes neither extensive fragmentation nor chemical change (chemical effect), such as change in the properties of the analyte.
However, when the analyte is a synthetic polymer or the like, the solubility of the analyte with respect to a solvent, the polarity of the polymer chain of the analyte, and the like greatly differ according to a difference in the chemical structure of the polymer chain. Further, even if the structure of the main chain is the same, the properties of the analyte differ according to the average molecular weight, the chemical structure of a terminal group, or the like. Therefore, it is necessary to optimize the kind of a matrix material and the method for preparing the crystal based on the kind of the analyte.
Further, a surface-assisted laser desorption/ionization mass spectrometry (SALDI-MA) method is being studied. In the SALDI-MA method, the matrix material is not used. Instead, a function for assisting desorption and ionization of the analyte is provided in the device for mass spectrometry per se to perform soft ionization. For example, the specification of U.S. Patent Application Publication No. 20080073512 and the specification of U.S. Patent Application Publication No. 20060157648 disclose a device for mass spectrometry using a porous silicon substrate having nano-order porous structure on the surface of the substrate. In the device, the interaction between the silicon nano-structure and the measurement light is utilized to perform soft ionization.
However, the degree of enhancement of the ion detection efficiency by the SALDI-MS method is not sufficient. Therefore, in mass spectrometry of a sparingly volatile substance and a high-molecular-weight substance, it is necessary to use high-power measurement light. Therefore, problems, such as fragmentation or change in the properties of the analyte, and deformation of the substrate per se, remain.